Coaxial transmission line fed electron gun

ABSTRACT

An electron-gun structure for wide bandwidth applications having a coaxial line input where the center conductor is the cathode heater and is provided with an internal transformer, the outer conductor is used to carry the signal to a modulating grid mounted near the cathode.

I United States Patent w: 3,596,129

[72] Inventor Ivan Cindrich [50] Field of Search 313/237, Southfield. Mich. 64, 82; 3 1 5/276, 1,3 [21] Appl. No 6,634 22 1 Filed ,la1|.28, 1970 1 New! Cited [45] Patented July 27, I971 UNITED STATES PATENTS {73] Assignee The United States 01' America as represented 3.374.387 3/1963 Schmid H by the Secretary of the Air Force I Pnmary Examiner-Roy Lake Assistant ExaminerV. Lafranchi Attorneys-Harry A. Herbert, Jr. and Henry S. Miller, Jr. [54] COAXIAL TRANSMISSION LINE FED ELECTRON GUN l 1 Damn ABSTRACT: An electron-gun structure for wide bandwidth [52] US. Cl 315/3, applications having a coaxial line input where the center con- 313/82, 313/237, 315/276 ductor is the cathode heater and is provided with an internal [51] Int. Cl. H0 1 j 1/02, transformer, the outer conductor is used to carry the signal to HOlj 23/16, HOlj 29/41; n01, 29/96, HOSb 41/24 a modulating grid mounted near the cathode.

PATENTFU JUL27 IQTI 'II a ma n WNW/4 T I //n//// 47 w v x COAXIAL TRANSMISSION LINE FED ELECTRON GUN BACKGROUND OF THE INVENTION This invention relates generally to electron beam devices and more particularly an electron gun for broad band applications in cathode-ray tubes and the like.

There are known electron guns that provide for wide band utilization. Generally these devices require a transfomicr for the cathode heater to provide sufficient numbers of electrons. In the prior art devices the transformers were mounted apart from the heater and where the electron gun was used in a cathode-ray tube, outside of the tube. This results in a substantially less satisfactory design where the device is fed with the coaxial transmission line. The electrical characteristics at the interface between the vacuum in the tube and the atmosphere outside show a degenerative effect on the production of electrons by the gun.

Prior coaxial transmission line fed electron guns utilized very nonrigid material and had an overall design apparently based on flexibility in the true sense, thereby causing the instruments to be delicate and highly susceptible to breakage maladjustment.

Additionally, older known devices utilize an oxide coated cathode which is difficult to produce in the unusually small size cathode that is desireable to obtain low cathode-to-grid capacitance needed for wide-bandwidth applications. Heretofore the prior art has resorted mainly to modifications of existing structures. To obtain high speed electron guns with a wide frequency diversification such as are needed, for wide bandwidth data recording for computer outputs and for data terminals as used to store data from various orbiting satellite data gatherers, a new approach has been needed and is believed to be provided in the instant invention.

This invention provides a means for changing the voltage between two electrodes of an electron gun in a manner which allows voltage changes at many different frequencies, for example from zero to Gl-lz.

One feature of the invention is the utilization of a coaxial transmission line fed electron gun where the transfonner used in the heater circuit is mounted inside the tube thereby avoiding the deleterious effects caused by the vacuum-atmosphere interface.

The invention further provides a physical structure that is strong and rugged in construction to provide a device with long life and accurate, reliable results.

The electron gun used in this invention utilizes a dispenser type cathode which easily lends itself to manufacture techniques which remaining small in size to produce a low cathode-to-grid capacitance.

Another feature of the invention is an improved method of supporting the cathode structure that is a substantial improvement over prior art devices in terms of transmission characteristics e.g. reflection coefficient.

[t is therefore an object of this invention to provide a new and improved coaxial transmission line fed electron gun.

It is another object of this invention to provide a new and improved transformer circuit for electron guns.

It is a further object of this invention to provide a new and improved means for supporting structural members in a coaxially fed electron gun.

It is still another object of this invention to provide a new and improved cathode structure for broad-bandwidth electron guns.

It is still a further object of this invention to provide an electron gun that is economical to produce and utilize conventional currently available components for ease and simplicity of construction.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodi ment in the accom an in drawin DETAILED ES RPTION FTHE PREFERRED EMBODIMENT Referring now to the FIGURE, the electron gun is shown located in the neck of a cathode-ray tube generally designated at 10. The input end of the tube 12 is adapted to connect to any well-known readily available coaxial line connector.

The outer conductor forms the outer wall of the structure 14 and ultimately terminates at the grid 16. The inner conductor l8 subsequently becomes the cathode 20.

Between the input to the tube and the final point of electron emission is a transformer shown generally as 22. The transformer consists of a primary winding 24 turned around the outer conductor 14. A slotted sleeve 26 is placed inside the outer conductor wall to add to the rigidity of the structure as well as to provide proper spacing for the supporting discs 28 and 30. The transformer located at this point and in this manner operates within the vacuum environment and can withstand high operating temperatures. One particular transformer has the capability of providing at least l5 watts of power to the cathode heater.

The supporting discs hold the inner conductor 18. Inside the inner conductor is the transformer core 32 around which is wrapped the secondary winding 34 of the transformerv The output of the transformer passes through the insulating disc 30 and into the center of the cathode 36 where it is connected to the heater 38. The cathode is attached to the support disc 30 by a metallized joint 40, while the secondary transformer leads are held by an insulating disc 42.

The cathode terminates with a small protrusion 44 extending away from the remainder of the structure forming the prirnary point for electron emission.

The part of the anode structure is shown in a conventional style at 46 in a position between the cathode and the cathoderay tube face (not shown).

The outer conductor forms a modulating grid 16 supported by the grid holder 48. A spacing sleeve 50 insures with great accuracy that the proper cathode-grid distance will be maintained.

In operation a signal pulse is applied at the input connector causing a voltage pulse to travel along the coaxial-line structure and appear between the modulating grid and cathode, where, if the signal has the proper polarity it will turn on the beam.

The overall structure is designed to be completely interchangeable with suitable electron beam devices. The ends 52, 54 of the outer conductor are fitted with female and male threads to allow for ease in removing the electron gun and making changes from one device to another. Likewise the inner conductor is mounted entirely within the outer conductor for accuracy in the spacing of the components and greater case in interchangeability.

Having thus described my coaxial transmission line fed electron gun it should be understood that the invention is subje to obvious modifications and variations within the skill of those in the art and the Inventor is not strictly bound by device as disclosed.

lclairn:

l. A coaxially fed electron gun for electron beam devices comprising: an inner conductor; and outer conductor surrounding the inner conductor; an elongated cylindrically shaped means connected to the inner conductor and terminating in a cathode; an anode, a transformer core, a secondary winding surrounding said core and terminating in a cathode heating element mounted inside said cylindrically shaped means; a primary transformer winding surrounding the outer conductor and positioned relative to said secondary winding to form a transformer; a grid connected to the outer conductor and placed between the cathode and the anode; and a pair of supporting discs, one for the inner conductor and the other one for the cathode. 

1. A coaxially fed electron gun for electron beam devices comprising: an inner conductor; and outer conductor surrounding the inner conductor; an elongated cylindrically shaped means connected to the inner conductor and terminating in a cathode; an anode; a transformer core, a secondary winding surrounding said core and terminating in a cathode heating element mounted inside said cylindrically shaped meanS; a primary transformer winding surrounding the outer conductor and positioned relative to said secondary winding to form a transformer; a grid connected to the outer conductor and placed between the cathode and the anode; and a pair of supporting discs, one for the inner conductor and the other one for the cathode. 